Ink jet nozzle

ABSTRACT

An ink jet nozzle comprises a unitary construction of a nozzle plate having a jewel orifice on one face with a passage through the plate at right angles thereto for supplying ink to the nozzle under pressure, a reaction mass and a piezoelectric ceramic connecting the nozzle plate and the reaction mass. The assembly is secured to a support by a silicone rubber isolation damper which permits the nozzle plate, piezoelectric ceramic, and the reaction mass to vibrate as a unit at a selected frequency to effect uniform break off of ink drops from the ink stream issuing from the nozzle.

Ble -334 51- United States Patent [1 1 Pimbley 1 INK JET NOZZLE [75]Inventor: Walter T. Pimbley, Vestal, NY.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Apr. 30, 1974 [21] Appl. No.: 465,632

OTHER PUBLICATIONS Denny et a1.; Diaphragm Ink Drop Generator And Dec.16, 1975 Liquid Horn; IBM Tech. Disc. Bulletin; Vol. 16, No. 3, August1973, pp. 789-791.

Newell, W. E.; Face-Mounted Piezoelectric Resonators; Proceedings of theIEEE, June 1965, pp. 575-581.

Primary Examiner-Joseph W. Hartary Attorney, Agent, or Firm-Francis V.Giolma [57] ABSTRACT An ink jet nozzle comprises a unitary constructionof a nozzle plate having a jewel orifice on one face with a passagethrough the plate at right angles thereto for supplying ink to thenozzle under pressure, a reaction mass and a piezoelectric ceramicconnecting the nozzle plate and the reaction mass. The assembly issecured to a support by a silicone rubber isolation damperwhich permitsthe nozzle plate, piezoelectric ceramic, and the reaction mass tovibrate as a unit at a selected frequency to effect uniform break off ofink drops from the ink stream issuing from the nozzle.

6 Claims, 13 Drawing Figures U.S. Patent Dec. 16, 1975 Sheet 1 of33,927,410

FIG. 5

US. Patent Dec. 16, 1975 Sheet 2 of 3 3,927,410

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L VOLTAGE US. Patent Dec. 16, 1975 Sheet30f3 3,927,410

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El E2 w 0251325 ADMITTANCE x 10 AMPS/ vou 00 100 FREQUENCY KHZ INK JETNOZZLE BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates generally to ink jet printers and it has reference inparticular to an ink jet nozzle structure and a method of making it.

2. Description of the Prior Art Ink jet nozzles are known such as shownin U.S. Pat. No. 3,334,351 which issued on Aug. 1, 1967 to N. L.Stauffer, showing schematically a right angle nozzle with amagnetostrictive transducer driving element for producing vibration ofthe nozzle.

US. Pat. No. 3,596,275 which issued on July 27, l97l to R. G. Sweet alsodiscloses schematically a similar right angle nozzle structure.

SUMMARY OF THE INVENTION Generally stated it is an object of thisinvention to provide an improved ink jet nozzle.

More specifically it is an object of the invention to provide an ink jetnozzle which is most efficient and effective within a predeterminedfrequency range.

It is an object of the invention to provide an ink jet nozzle which hasimproved ink drop forming characteristics.

It is also an object of the invention to provide an ink jet nozzle inwhich a resonant perturbation condition is attained, so as to enhancethe formation of uniform ink drops from an ink stream.

Yet another object of the invention is to provide a sandwich type nozzlestructure wherein a piezoelectric ceramic for producing perturbations inan ink stream is secured between a nozzle plate and a reaction mass tovibrate as a unit at a selected frequency.

It is also an object of the invention to provide for defining therelative proportions of a nozzle plate, a piezoelectric ceramic and areaction mass in an ink jet nozzle structure for the most efficientoperation thereof.

Still another object of the invention is to provide for securing anozzle plate, piezoelectric ceramic, and a reaction mass together bycementing them together with a predetermined wire spacer in the cementbetween the parts to insure consistently accurate relative positioningof the elements.

Yet another important object of the invention is to provide for securinga unitary structure of a reaction mass, a piezoelectric ceramic, and anozzle plate, to support means by means of a silicone rubber compositionwhich provides a damped connection, permitting the unitary structure tofloat and vibrate as a unit, independently of the mass of the supportmeans.

A further object of this invention is to provide for determining therelative proportions of a multielement nozzle structure for operation ina predetermined frequency range.

A still further important object of the invention is to provide anintegrated ink jet nozzle structure wherein the perturbance velocityamplitude is proportional to the current of the exciting signal.

The foregoing and other objects, features and advantages of theinvention will be more apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of an ink jetnozzle structure embodying the invention.

FIG. 2 is a partial cross-sectional view of the nozzle plate and ceramicof FIG. 1. 1

FIG. 3 is an isometric view of the nozzle plate piezo electric ceramicand reaction mass.

FIG. 4 is an enlarged partial cross-sectional view of the assembly inFIG. 3 showing how the elements are cemented together.

FIG. 5 is a schematic showing of the equivalent electric circuit of theassembly shown in FIG. 3.

FIG. 6 is a curve showing the relationship between the admittance andthe frequency of oscillation for the nozzle structure of the invention.

FIG. 7 is a curve showing the relationship between the phase andfrequency for the equivalent circuit and the actual nozzle structure ofthe invention.

FIG. 8 is a curve showing the relationship between break off time versusvoltage at 60 KHz.

FIG. 9 is a curve showing the relationship between break off timeandvoltage at lOO'KHz.

FIG. 10 is a curve showing the reciprocal of the break off time versusthe wave length for 60 KHz.

FIG. 11 is a curve showing the reciprocal of the break off time versuswave length for KHz.

FIG. 12 is a curve showing the relationship between the velocityperturbation per volt versus the frequency.

FIG. 13 is a curve showing the relationship between the velocityperturbation per volt versus the admittance.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1 the referencenumeral 10 denotes generally an ink jet nozzle structure comprising arectangular nozzle plate 12 cemented to a piezoelectric ceramic 14,which is in turn cemented to a reaction mass 16. The nozzle plate 12comprises a generally rectangular plate of stainless steel having apassage 18 entering from one side by means of a nipple 20 to which aflexible hose may be fastened for supplying ink to the passage 18 underpressure. Pressures in the range of 30 to 60 pounds may be used. Theplate is provided with an opening 22 at the center connecting with thepassage 18, and over which a jewel nozzle 24 may be secured in anysuitable manner such as by cementing, the nozzle having a centralorifice 26 which is perpendicular to the passage 18 and through which astream of ink may be projected under pressure. The passage 18 may have adiameter on the order of 0.030 inches by way of example.

The nozzel plate 12 is secured to one face of a piezoelectric ceramic14, the other face of which is secured to a reaction mass 16 'which maycomprise a generally rectangular block of stainless steel for example.The reaction mass is secured to a generally U-shaped support 30 having acentral bight portion 32 with upstanding spaced apart legs 34, and 36having projecting tabs 38 and 40 at the ends to which flat springs 42and 44 may be connected by means of screws 46 and 48 for fastening theassembly to lugs 50 and 52 on the frame of the printer and permittingmovement for aiming. An arm 54 projecting from the central portion ofthe bight 32 may be used with suitable adjusting means (not shown) foraiming the nozzle 24 and directing the ink stream.

As shown in FIG. 4 the nozzle plate 12 and the reaction mass 16 may becemented to the piezoelectric ceramic 14 by means of layers of cement land 16 comprising for example an epoxy cement. In order to provide thebest bond between the nozzel plate, the reaction mass and the ceramic,it is essential that the layers of cement 15 and 16 be accuratelydefined. For this purpose Molybdenum wire spacers, 0.003 inches indiameter identified by the numeral 19 may be imbedded in the epoxy. Thesandwiched structure is then cured while being held in a springloadedjig, the wires 19 maintaining perfect spacing between the elements.

The reaction mass 16 is secured to the support by means of siliconerubber 56 having a durometer value of 65 for example, on the Shaw scale,and which is bonded to the bight and to the two legs of the support 30,as well as to the reaction mass 16. The thickness of the rubber 56 isnot critical and any value from a few mils to about A inch may be used.This permits the assembly of the nozzle plate 12 ceramic l4 and reactionmass 16 to float and vibrate independently of the mass of the support30. Connectors 58 and 60 may be connected to the reaction mass 16 andthe nozzle plate 16 for applying a voltage therebetween to effectvibration of the piezoelectric ceramic thus causing the nozzle plate andthe nozzle to vibrate longitudinally relative to the ink stream thusimposing the velocity perturbation thereon.

The frequency of response of an ink jet head can be obtainedapproximately by considering the response of three semi-infinite slabsadjacent to one another such as shown in FIGS. 3 and 4. Media I and IIIrepresent the nozzle plate 12 and the reaction mass 16, respectively andMedium II represents the piezoelectric ceramic l4. Thickness modevibrations of the ceramic slab 14 cause longitudinal standing waves tobe set up in all three media in the x directions shown.

The controlling wave equation for this physical problem is and v v and vthe velocities of the waves in the media are given by:

There are six unknowii constants in equatidii through Cg: Theseconstants will be determi'riecl by boundary conditions. At theboundaries A and D in FIG. 3 the force transmitted per unit area equalszero. At boundaries B and C, u, the displacement is continuous. Also atboundaries B and C, the force per unit area which is transmitted isdiscontinuous; the discontinuity at the two boundaries being equal inmagnitude but opposite in direction. This discontinuity is given by:

H and H are the acoustic impedance mismatches between media I and II andII and III respectively. They are given by:

where A A and A are the areas of the three media. The parameters thatmatch the head shown in FIG. 4

are:

L =O.O9O inch, L =O.25O inch, L =O.25O inch, v,=v =l.97 lO inches sec. v=l.O6 l0 inches/sec.

The first four resonant frequencies, as computed from equation (6), are:

101.6 KHZ f =238.4 KHZ f 365.7 KHZ .,=473.2 KHz The frequencycharacteristics of the head shown in FIG. 1 were measured. FIG. 6 showsthe admittance curve for the head while FIG. 7 shows the phasedifference versus frequency. In both figures the points representexperimental data and the solid line is the result of the fittedequivalent circuit shown in FIG. 5. Of course, the equivalent circuitwould only fit in the given frequency range 30 KHz to KHz. The measuredfirst mechanical resonance is 103.3KHz and the corresponding parallelresonance point is 120.5KI-lz.

Break-up of Ink Stream Into Drops.

In order to design properly an ink jet heat, one must be able to relatethe performance of the ink stream breakup properties back to the initialperturbation imposed on the stream by the head. Lord Rayleigh firstpresented an analysis that would provide a relationship required.However, the initial conditions used by him are not suitable to thepresent problem. A variation of the analysis will therefore beconsidered.

It is possible to show the variation of the analysis using a onedimensional model; Assume a stream of liqiiid initially in the shape ofa cylinder in which the radius, longitudinal velocity of the stream, andpressure in the liquid are functions oft, time, and 2, one dimension,only. Further assume that the relative coordinate system is such thatthe DC velocity of the stream is zero. The two differential equationsthat describe the break-up of the stream into drops are:

111 dz p 112 (9) r2 dv dr dr dz v dz d! 0 For the initial conditions,set:

r=a v=v ,Sinkz (11) where:

a and v are constants, A is the wave length for the imposedperturbation. The solution to the described prob lem, whenapproximations are made to linearize the problem, is:

v v Sin kz Cosh ut These equations show Lord Rayleighs conclusion. If akis less than one, u is real and the radial disturbance grows until dropbreak-off occurs. If, however, the wave length of the disturbance isless than the original circumference of the stream (a k greater thanone), the hyperbolic functions become circular functions and anequilibrium condition would occur.

v is the amplitude of the perturbation imposed on the stream by the inkjet head. However, the break-up properties of the stream are dependenton all of the other parameters of the analysis as well. The analysis isused, therefore, to relate the observed properties of stream break-up tov thus eliminating the influence of the other parameters.

6 The break-off time is measured by measuring the break-off distance anddividing by the velocity of the stream. v can then be found fromequation 14 by assuming that r O at some point at the break off time.Thus:

where I is the break off time.

Numerous sets of data were taken to show the characteristics of the inkjet head. FIGS. 8 and 9 show the break-off time as a function of thelogarithm of the voltage amplitude of the impressed signal at constantfrequency and wave length. From the straight line relationship, one cansay:

where V. is the voltage amplitude and c and b are constants. Acomparison with equation 16 shows that in the range given theperturbation, v is directly proportional to the imposed electric signal.Furthermore, c in equation 17 equals u in equation 16. The ink jet headshould always be operated in the linear region where the perturbation isproportional to the signal for satisfactory operation.

Sets of data have been taken for the break-up time as a function of wavelength; frequency and head excita tion being kept constant. The wavelength was controlled by changing the ink pressure which caused thestream velocity to change. FIGS. 10 and 11 show two of the sets of datataken. The points represent the experimental data, while the solid lineis the theoretical curve from equations 13 and 15. The initialperturbation amplitude, v is chosen so as to provide the best fit.

FIG. 12 is a graph showing the perturbing velocity amplitude per volt ofexciting signal as a function of the frequency. The solid line is just asmooth curve drawn through the points. FIG. 13 shows the same dependentvariable plotted against the admittance of the ink jet head, with astraight line being drawn through the data. The slope of the straightline on this log-log plot is one, showing a direct proportionalitybetween the current through the head and the resulting perturbation.

The result that the perturbing velocity amplitude is proportional to theexciting signal is most important. This proportionality depends on therelatively short length of the liquid cavity parallel to the axis of thehead. Others have shown that when the cavity is one quarter wave lengthlong when acting as an open ended tube, or a half wave length whenacting as a closed tube, (wave length measured in liquid) a resonancethat enhances drop break off occurs. Such a resonance would probably notmanifest itself as an admittance change back at the piezoelectricceramic.

A commercial, one compound epoxy is used to bond the piezoelectricsandwich. The curing cycle for the epoxy is heating at 250F for 2 hours.While the epoxy is warming up it passes through a stage where it flowsquite freely. Since the epoxy layer should be from 7 0.001 to 0.005inches thick for the best result the Molybdenum wire spacers 19, 0.003inches in diameter, are imbedded in the epoxy to insure uniformthickness since the sandwiches are cured while being held inspring-loaded jigs.

An ink jet head structure has been disclosed that uses a piezoelectricsandwich concept with the nozzle in the front plate. The vibration ofthe front nozzle plate and the nozzle longitudinally with the streamcauses the stream break-up action. The head is relatively fiat and canbe used separately or can be packaged in densities of up to six headsper inch. Enough room exists between heads to permit individual aimingof the heads.

For different frequency applications the resonant point may be shiftedby an appropriate choice of longitudinal dimensions. An equation hasbeen presented, equation 6, so that required dimensions may becalculated.

A variation of theory has been presented which relates the dropbreak-off characteristics with the per turbing velocity amplitude at thenozzle. Thus the action of the head on the jet can be observedindependently of the action of the jet after it leaves the nozzle.

The perturbing velocity amplitude has been shown to be directlyproportional to the current amplitude of the exciting signal. Therefore,with the use of a constant current source, a network in series with thehead to provide constant current or a feedback loop to control current,the response of the head can be made level.

While the invention has been shown and described with reference to apreferred embodiment thereof, it will be understood by those skilled inthe art that various changes in form and details may be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. In an ink jet printer apparatus,

a support member,

a substantially flat ink jet nozzle structure disposed for connection toa source of ink,

a reaction mass,

damping means resiliently connecting said reaction mass to said supportmember, and

transducer means operating in a thickness mode connecting said nozzlestructure to said reaction mass for producing resonant periodic bodilyvibration of said nozzle and reaction mass independently of said supportmember to produce periodic drops of ink from said nozzle.

2. The invention as defined in claim 1 characterized by said ink jetnozzle structure comprising a plate having a nozzle opening on onesurface and an opening through said plate at right angles to said nozzleopening for supplying ink thereto under pressure.

3. The invention as defined in claim 2 characterized by said transducermeans comprising a piezoelectric crystal plate sandwiched between saidnozzle plate and one surface of said reaction mass.

4. The invention as defined in claim 3 characterized by said nozzleplate, piezoelectric crystal, and reaction mass being cemented to eachother in a sandwich arrangement by layers of epoxy resin with wirespacers included in said layers to maintain a predetermined uniformthickness of said layersv 5. The invention as defined in claim 3characterized by said damping means comprising a body of silicone rubbersecured to said support member and to and partially surrounding saidreaction mass on two opposite sides and the intervening surface awayfrom the surface secured to said piezoelectric crystal.

6. The invention as defined in claim 3 characterized by the relativethicknesses of the nozzle plate, piezo electric crystal, and reactionmass being related by the formula Cos k L [Sin k L Cos k L H Cos k L Sink L H Sin k L [Cos k L Cos k L H Sin k L Sin k L 0 where L L and L, arethe thicknesses of the nozzle plate, piezoelectric crystal and reactionmass, respectively; H and H are the acoustic impedance mismatchesbetween the nozzle plate and piezoelectric crystal, and thepiezoelectric crystal and reaction mass respectively; and k k and kequal w/v (ii/v and (D/V3, where v,, v and v are the velocities of thewaves in the media of the nozzle plate, piezoelectric crystal andreaction mass, respectively.

1. In an ink jet printer apparatus, a support member, a substantiallyflat ink jet nozzle structure disposed for connection to a source ofink, a reaction mass, damping means resiliently connecting said reactionmass to said support member, and transducer means operating in athickness mode connecting said nozzle structure to said reaction massfor producing resonant periodic bodily vibration of said nozzle andreaction mass independently of said support member to produce periodicdrops of ink from said nozzle.
 2. The invention as defined in claim 1characterized by said ink jet nozzle structure comprising a plate havinga nozzle opening on one surface and an opening through said plate atright angles to said nozzle opening for supplying ink thereto underpressure.
 3. The invention as defined in claim 2 characterized by saidtransducer means comprising a piezoelectric crystal plate sandwichedbetween said nozzle plate and one surface of said reaction mass.
 4. Theinvention as defined in claim 3 characterized by said nozzle plate,piezoelectric crystal, and reaction mass being cemented to each other ina sandwich arrangement by layers of epoxy resin with wire spacersincluded in said layers to maintain a predetermined uniform thickness ofsaid layers.
 5. The invention as defined in claim 3 characterized bysaid damping means comprising a body of silicone rubber secured tO saidsupport member and to and partially surrounding said reaction mass ontwo opposite sides and the intervening surface away from the surfacesecured to said piezoelectric crystal.
 6. The invention as defined inclaim 3 characterized by the relative thicknesses of the nozzle plate,piezoelectric crystal, and reaction mass being related by the formulaCos k1 L1 (Sin k2 L2 Cos k3 L3 + H3 Cos k2 L2 Sin k3 L3) + H1 Sin k1 L1(Cos k2 L2 Cos k3 L3 -H3 Sin k2 L2 Sin k3 L3) 0 where L1 L2 and L3 arethe thicknesses of the nozzle plate, piezoelectric crystal and reactionmass, respectively; H1 and H3 are the acoustic impedance mismatchesbetween the nozzle plate and piezoelectric crystal, and thepiezoelectric crystal and reaction mass respectively; and k1 k2 and k3equal omega /v1 omega /v2 and omega /v3, where v1, v2 and v3 are thevelocities of the waves in the media of the nozzle plate, piezoelectriccrystal and reaction mass, respectively.